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Showing posts with label Castables. Show all posts
Showing posts with label Castables. Show all posts

Benefits of using Steel Fibers and Organic Fibers in Refractory Castables and Monolithics

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One of the most effective ways of improving the mechanical and thermal properties of refractory castables and other monolithic refractories is adding in suitable proportions of stainless steel fibers (SS) and organic fibers to the castable respectively.

Steel Fibers
Steel fiber reinforced refractory castables are very resistant to the tendency of the material to fall apart on thermal cycling. Stainless steel fibers greatly improve the flexural strength of the castable. And this added increase in ductility contributes significantly to the thermal shock and spalling resistance of the material. The fibers generally used are in size varying between 0.1 to 0.4 mm2 in cross-section & 20-40 mm in length. For monolithic SS is used either high chrome or high chrome nickel steels available in the market with different grades. One reason commonly reported that the thermal shock resistance of castables is greatly increased through addition of SS fibers because these fibers act as crack arresters, preventing cracks propagating. This is also possible that the microcracks caused by a mismatch in thermal expansion coefficients of matrix and fibers dissipate energy from larger cracks propagating as a result of thermal stress. However percentage of these fibers added becomes important because of two reasons as it has a direct impact on the fluidity of the castable, then it may also cause mixing difficult due to fiber-balling when added beyond 3% by volume. Another critical factor will be the maximum application temperature for the castable that those fibers present in the castable can resist oxidation (since these fibers can not perform beyond their melting temperature).

Organic Fibers

An effective means for improving the explosive spalling resistance of a castable is to add organic fibers to the formulation. It has been reported that the composition & concentration of fibers are not as important as melting temperature of the fiber, since these fibers after melting increase permeability at certain temp. & thereby reducing the explosive spalling tendency of the castables. The fibers generally used for this purpose are Polypropylene fibers, Polyester staple fibers, etc.

Here is one reference (work) of benefits of using refractory composition containing both stainless steel fibers and organic fibers. Because of these different advantages it have been found that both organic and SS fiber reinforced refractory castables provide substantial increase in service life and therefore, a considerable reduction in refractory maintenance cost and furnace down-time.
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